Method of making composite nickel electroplate and electrolytes therefor

ABSTRACT

A COMPOSITE NICKEL-CONTAINING ELECTROPLATE IS FORMED ON A BASE METAL SURFACE BY ELECTROPLATING ON THE SURFACE AN ADHERENT NICKEL OR NICKEL ALLOY LAYER HAVING A THICKNESS OF FROM ABOUT 0.15 TO 1.5 MILS AND AN AVERAGE SULFUR CONTENT OF LESS THAN ABOUT 0.03%. AN INTERMEDIATE NICKEL OR NICKEL ALLOY LAYER, HAVING A THICKNESS OF FROM ABOUT 0.005 TO 0.2 MILS AND AN AVERAGE SULFUR CONTENT OF FROM ABOUT 0.05 TO 0.3% IS THEN ELECTROPLATED ON THE LOWER LAYER, AN ADHERENT UPPER NICKEL OR NICKEL ALLOY LAYER HAVING A THICKNESS OF FROM ABOUT 0.2 TO 1.5 MILS AND AVERAGE SULFUR CONTENT OF FROM ABOUT 0.02 TO 0.15% IS THEN ELECTROPLATED ON THE INTERMEDIATE LAYER, THE UPPER LAYER CONTAINING A LOWER PERCENTAGE OF SULFUR THEN THE LOWER LAYER. THE SOURCE OF SULFUR, FOR AT LEAST THE INTERMEDIATE LAYER, IS PROVIDED BY INCLUDING NOVEL THIOSULFONATED OF NITRILES OF AMIDES IN THE PLATING BATH FOR THE LAYER.

US. Cl. 204-40 20 Claims ABSTRACT OF THE DISCLOSURE A compositenickel-containing electroplate is formed on a base metal surface byelectroplating on the surface an adherent nickel or nickel alloy layerhaving a thickness of from about 0.15 to 1.5 mils and an average sulfurcontent of less than about 0.03%. An intermediate nickel or nickel alloylayer, having a thickness of from about 0.005 to 0.2 mils and an averagesulfur content of from about 0.05 to 0.3% is then electroplated on thelower layer. An adherent upper nickel or nickel alloy layer having athickness of from about 0.2 to 1.5 mils and average sulfur content offrom about 0.02 to 0.15% is then electroplated on the intermediatelayer, the upper layer containing a lower percentage of sulfur then thelower layer. The source of sulfur, for at least the intermediate layer,is provided by including novel thiosulfonates of nitriles or amides inthe plating bath for that layer.

This application is a continuation-in-part of application Ser. No.862,942, filed Oct. 1, 1969 and now abandoned.

The present invention relates to an improved process for forming acomposite electroplate on a metal base and more particularly, it relatesto improvements in the method of forming a composite electroplatecomprising three types of nickel electroplates which are adjacent orcontiguous to each other and to a plating bath useful in this process.

In US. Pat. 3,090,733, issued May 21, 1963 to Henry Brown, there isdescribed an improved composite electroplate on a base metal which ismade up of three types of nickel electroplate that are adjacent orcontiguous to each other and the method of preparing this improvedcomposite coating. As disclosed in this patent, this compositeelectroplate is made up of three adjacent bonded layers of nickel eachhaving a certain thickness with the intermediate layer of nickel havinga higher sulfur content than the nickel layers which sandwich it and theupper layer of nickel having an appreciably higher sulfur content thanthe lower layer.

As is set forth in this patent, various inorganic and organic sulfurcontaining compounds may be incorporated in the plating baths from whichthe intermediate and upper nickel layers are produced to provide thedesired sulfur content in these layers. Included as examples of thesulfur compounds which may be used are various thiosulfates, sulfites,bisulfites, hyposul-fites, hydrosulfites, sulfoxylates, sulfinates,thiocyanates, sulfoxides, sulfonic acids, mercapto aromatic acids,thioureas, isothioureas, thiohydantoins, sulfonamides, sulfonimides,sulfonyl halides, sulfones, and the like.

Although by the process of this patent, greatly improved corrosionprotection is obtained, even with a much thinner total thickness ofnickel plate, than has heretofore been possible, some difiiculties havebeen encountered with the operation of this process. Thus, when usingthe United States Patent sulfur containing additives disclosed in thispatent, it is found that the plating baths are sensitive to airagitation, and to high temperatures, thus limiting the speed at whichthe plating operation can be carried out. Additionally, the electrolyticremoval of metal contaminates such as zinc, copper and lead, which buildup in the plating bath, i.e., the dummying out of these metals, cannotbe effected until the sulfur containing additives have been decomposedby oxidation. This, therefore, means that after the dummying out ofthese metals, the sulfur compound additives must be replenished in theplating baths before the plating operation can be resumed. This is, ofcourse, is both time consuming and costly.

It is, therefore, an object of the present invention to provide animproved process for forming a three layered composite nickel containingelectroplate which may be carried out at faster plating speeds and fromwhich metal impurities may be electrolytically removed, withoutdestroying the sulfur compound additives in the bath.

A further object of the present invention is to provide an improvedelectroplating bath for use in the present piocess for forming the threelayered composite electrop ate.

These and other objects will become apparent to those skilled in the artfrom the description of the invention which follows.

[Pursuant to the above objects, the present invention includes animprovement in the process of forming a composite nickel containingcoating on a corrosion susceptible base metal surface by electroplatingon said surface an adherent lower layer of a nickel containingelectroplate having a thickness of from about 0.15 mil to 1.5 mils andan average sulfur content of less than about 0.03%, electroplating onsaid lower layer an adherent intermediate layer of a nickel containingelectroplate having a thickness of from about 0.005 to about 0.2 milsand an average sulfur content of from about 0.05 to 0.3% andelectroplating on said intermediate nickel containing layer an adherentupper layer of a nickel containing electroplate having a thickness offrom about 0.2 to 1.5 mils and an average sulfur content of from about0.02 to 0.15%, said upper layer containing a lower percentage of sulfurthan said intermediate layer and a higher percentage of sulfur than saidlower layer, which improvement comprises including at least onethiosulfonate of nitriles or amides in the electroplating bath as thesource of sulfur in at least the intermediate nickel containing layer.By the use of thiosulfonates of nitriles or amides, rather than othersulfur containing compounds, such as those set forth in US. Pat.3,090,733, it is found that the plating baths may be operated with airagitation, and higher temperatures, thus making possible faster platingspeeds, and metallic impurities, such as zinc, copper, and lead, may beelectrolytically removed from the plating bath without the need forfirst destroying these sulfur containing compounds by oxidation.

More specifically, in the pratice of the present invention,thiosulfonates of nitriles or amides are incorporated in at least theelectroplating bath used for forming the intermediate nickel containinglayer, to provide the source of sulfur in the intermediate layer and,preferably, are included in the electroplating baths for both theintermediate and the upper nickel containing layer, to provide thesource for the sulfur in these layers. As has been noted hereinabove,sulfur content of the immediate nickel containing layer is desirablywithin the range of about 0.05 to 0.3% while that in the upper nickelcontaining layer is desirably within the range of about 0.02 to 0.15%Accordingly, the thiosulfonates of nitriles or amides are desirablyincorporated in the plating baths used to produce these layers inamounts within the range of about 0.01 to 0.4 grams per liter, withamounts within the range of about 0.03 to 0.1 grams per liter beingpreferred in the electroplating baths used to produce the intermediatelayer and amounts within the range of about 0.01 to 0.04 grams per literbeing preferred to the electroplating bath from which the upper layer isproduced. Obviously, the exact amount of these thiosulfonates ofnitriles or amides incorporated in the electroplating baths will dependupon the particular compound or compounds which are used, so that insome instances, amounts of these materials which are either greater thanor less than the preferred ranges indicated may also be used, so long asthe particular amounts of these compounds which are used are sufficientto provide the desired amount of sulfur in the particular nickelcontaining electroplated layer.

The novel thiosulfonates of nitriles or amides which may be used in thepresent process are represented by the following formulae:

atoms and R is either an alkylene group containing from 2 to 6 carbonatoms or a group containing the following structure:

wherein R is an alkyl group containing from 2 to 4 carbon atoms. R and Rindependently may be hydrogen or alkyl of from 1 to 4 carbon atoms; X isor 1. In general, these compounds may be prepared by the reaction of amercapto alkyl sulfonate with an unsaturated nitrile or an amide by theaddition of the mercapto group across the double bond of the unsaturatednitrile or amide. The process takes place preferably in the presence ofa copper catalyst although one may not be used. The reaction normallytakes palce in an aqueous system in basic media, preferably having a pHof from 7.5 to 10.

Exemplary of such products which may be used in the present process arethe following:

When 50; is used, it is meant to include sulfonic acid and its watersoluble salts. Other suitable products are those where R is --(CH orwhere R is ethyl, propyl, butyl, isobutyl or tertiary butyl; or where Ror R are methyl, ethyl, propyl or butyl. Of these, particularly goodresults have been obtained when using the reaction product of mercaptanpropane sulfonate and dicyanobutene or acrylonitrile. Accordingly,although specific reference maybe made hereinafter to these materials asbeing preferred for use in the present method, this is not to be takenas a limitation on the thiosulfonates of nitriles or amides which may beused but merely as being exemplary of those materials.

The three-layered nickel composite coating produced by the method of thepresent invention may be made with a dull Watts nickel as the lowerlayer and a dull, semi-bright or bright nickel as the upper layer,provided that the upper layer has, as has been previously indicated, ahigher sulfur content than the bottom layer. Although improved corrosionprotection is obtained with this 3-layer nickel containing coating inthe absence of a final chromium plate, in many instances it is preferredthat the upper nickel layer is covered with a final thin brightconventional chromium, or micro-cracked or microporous chromium plate,desirably of a thickness of from about 0.005 to 0.2 mils. In general, ithas been found desirable that the lower nickel containing layer bethicker than the upper layer, the preferred ratio being from about 50:50to :20 to obtain the best ductility of the cbating. Where, however,ductility is not of primary concern, the lower layer may be thinner thanthe upper nickel containing layer, ratios of about 40:60 being typical,and still obtain excellent corrosion protection of the base metalsurface.

It is to be appreciated that in addition to the sulfur, the nickelcontaining layers making up the composite coating of the presentinvention may also contain small percentages of other components as aretypically present in such coatings, such as carbon, selenium, tellurium,zinc, cadmium, iron and the like. Additionally, these nickel containinglayers may also contain appreciable quantities of cobalt, e.g., amountsup to at least as high as 50% cobalt may be present in the nickelcontaining electroplate layers. Frequently, however, it has been foundto be desirable that the lower nickel containing electroplate be as purenickel as possible.

Accordingly, the lower nickel containing electroplate may be producedfrom a Watts-type nickel plating bath, a fiuoroborate, a high chloride,a sulfamate nickel plating bath or a substantially sulfur-freesemi-bright nickel plating bath. The electroplating baths from which theintermediate nickel containing plate is deposited may be of the sametype used for the deposition of the lower nickel containing plate or itmay be an alkaline nickel electroplating bath or a high sodium,ammonium, lithium or magnesium content type nickel plating bath. Thebaths from which this intermediate nickel containing electroplate isproduced will, of course, contain one or more of the thiosulfonates ofnitriles or amides, in the amounts which have been indicatedhereinabove, to provide the amount of sulfur which is desired in thisintermediate layer. Similarly, the electroplating baths from which theupper nickel plate is deposited may be similar to those used for platingthe intermediate layer except, of course, that the concentrations of thesulfur compound, such as the thiosulfonates of nitriles of amides, willbe lower than those used in the bath for plating the intermediate layer.Moreover, where it is desired to provide a decorative plate, the uppernickel containing layer is desirably produced from a bright nickelplating bath that employs one or more of the organic sulfo-oxy compoundsset forth in Table II of U.S. Pat. 2,512,280 and Table II of U.S. Pat.2,800,440, which compounds are also preferably used with unsaturatedcompounds or amines to give both leveling and brillance.

These plating baths may also contain other components, such as wettingagents to prevent pitting, buffers, such as boric acid, formic acid,citric acid, acetic acid, :fluoboric acid, and the like. These platingbaths may typically be operated at temperatures within the range of fromabout room temperature, i.e., about 20 degrees C., to at least about 85degrees C. and at pH values for acidic baths within the range of about1-6. It is to be appreciated that the electroplating baths of thepresent invention will be operated in the manner set forth in U.S. Pat.3,090,733 to produce the composite nickel-containing three-layeredcoating. It is found, however, that by using the particular sulfurcontaining compounds which have been described hereinabove, rather thanthose compounds set forth in the issued patent, faster plating speedsare possible, through the use of air agitation, and higher temperatures,and

' metal impurities, such as zinc, copper and lead may beelectrolytically removed from the plating baths without first destroyingthe organic sulfur compounds. Thus, it is seen that the process of thepresent invention may be operated in the manner as set forth in U.S.3,090,733 to provide a three layered nickel plate on steel, aluminum,zinc, magnesium, brass, and similar base metals which are susceptible tocorrosion but represents an improvement over the process set forth inthat patent through the use of certain specific and particular sulfurcontaining compounds which have been found to be unique when compared tothe compounds typically disclosed in the patent.

In order that thosse skilled in the art may better understand thepresent invention and the manner in which it may be practiced, thefollowing specific examples are given. In these examples, unlessotherwise indicated parts and percent are by weight and temperatures arein degrees centigrade.

EXAMPLE 1 Preparation of compositions One mole of mercapto propanesulfonic acid was placed in one liter of water and was adjusted to a pHof 8.5 with the addition of caustic. To this solution is added 5 gramsof copper acetate and 1.1 moles of acrylonitrile and heated to 45 C.whereupon an exotherm occurs and the solution temperature rises to 80 C.After about 2 hours, the reaction is completed whereupon the residualunreacted acrylonitrile is removed by vacuum.

In a similar manner, mercapto propane sulfonate will react with 1,4dicyanobutene, iacrylamide land N-tentabutyl acrylamide.

EXAMPLE 2 Steel panels were plated with a three layered nickel system asfollows:

15 ,um. (0.6 mil) of sulfur free semi-bright nickel having a sulfurcontent of 0.003%.

1.5 ,um. (0.06 mil) of high sulfur content nickel having a sulfurcontent of 0.143% provided by a concentration of 0.05 g./l. of di cyanobutene mercapto propane sulfonate in an air-agitated nickel solutionoperated at 145 F.

10 m. (0.4 mil) of bright nickel having a sulfur content This depositwas chromium plated with 0.25 mm. (0.01 mil) of chromium andsubsequently exposed to the Corrodkote accelerated test. After 16 hoursone failure point developed whereas similar panels without the highsulfur intermediate layer developed in excess of 25 failure sites.

EXAMPLE 3 A deposit similar to that described in Example 2 was preparedexcept that the concentration of the dicyanobutane mercapto propanesulfonate was increased to 0.1 g./l. The sulfur content of theintermediate deposit was increased to 0.22%. The three layerednickel-chromium deposit again was substantially superior to a deposit ofsimilar thickness which omitted the thin high sulfur intermediate layer.

EXAMPLE 4 Panels were plated with the three layered nickel system asfollows:

10 ,um. (0.4 mil) of sulfur free semi-bright nickel having a sulfurcontent of 0.003%.

1.75 m. (0.07 mil) of high sulfur content nickel having a sulfur contentof 0.16% provided by a concentration of 0.09 g./l. of nitrilo propanemercapto propane sulfonate in an air-agitated nickel solution having asolution temperature of 140 F.

10 mm (0.4 mil) of bright nickel having a sulfur content This depositwas chromium plated with 0.25 am. (0.01 mil) of chromium andsubsequently exposed to the CASS test. After 20 hours, no points ofpenetration to the basis metal developed whereas similar panels withoutthe high sulfur intermediate layer had in excess of 14 failure points.

EXAMPLE 5 Panels were prepared with the three layered nickel depositsand chromium exactly as described in Example 1 except that the highsulfur deposit was plated from (1) a non-air agitated Watts type nickelsolution at F. using 0.2 g./l. of benzene sulfinate (U.S. Pat. No.3,090,- 733), and (2) an air agitated Watts type nickel solution at 145F. using 0.045 g./l. of dicyanobutane mercapto propane sulfonate.

Upon exposure to 32 hours of the Corrodkote accelerated test the panelsplated with the high sulfur strike utilizing benzene sulfinate developed100 points of failure to rust, while the panels plated with the highsulfur strike utilizing the dicyanobutane mercapto propane sulfonatedeveloped about 25 points of failure.

EXAMPLE 6 Comparative tests on the stability of addition agents used inExamples 5(1) and 3, in hot nickel solutions, showed the following:

(1) After being held for 16 hours in a nickel solution at a pH of 1.5and a temperature of F., 47% of the benzene sulfinate present wasoxidized while (2) After being held 24 hours under similar conditions noloss of the nitrilopropane-mercapto propane sulfonate occurred.

EXAMPLE 7 In order to test the plating ability of the compounds of thepresent invention an air agitated Watts nickel bath having a pH of 2.2was prepared. The reaction product of mercapto propane sulfonate andN-tertbutyl acrylamide (compound #8) was placed in the bath at aconcentration of 40 mg./l. Into a similar bath at an equal concentrationwas placed the reaction product of mercapto propane and acrylamide(compound #3). The results indicated that the N-tertbutyl material wasmore ductile than the acrylamide product but was not as lustrous. Byadding 0.25 g./l. of saccharin to each bath, the sulfur content wasraised to 0.082%. The plating results showed that the baths were equal.

While there have been described various embodiments of the invention,the specific compositions and processes set forth herein are not to betaken as limiting the scope of this invention but merely as beingexemplary thereof.

What is claimed is:

1. In the process for forming a corrosive protective composite threelayered nickel containing coating on a corrosion susceptible base metalsurface by electroplating on said surface an adherent lower nickelcontaining layer having a thickness of from about 0.15 to 1.5 mils andan average sulfur content less than about 0.03%, electroplating on saidlower layer an adherent intermediate nickel containing layer having athickness of about 0.005 to 0.2 mil and an average sulfur content ofabout 0.05 to 0.3% and electroplating on said intermediate layer anadherent upper nickel containing layer having a thickness of from about0.2 to 1.5 mils and an average sulfur content of about 0.02 to 0.15%,said upper layer containing a lower percentage of sulfur than saidintermediate layer and a higher percentage of sulfur than said lowerlayer, the improvement which comprises including in the electroplatingbath from which at least the intermediate nickel containing layer isproduced, a thiosulfonate of nitriles or amides as the source for thesulfur contained in said layer, said thiosulfonate being selected fromthe group consisting of:

wherein R is an alkylene group containing 2 to 4 carbon atoms; R iseither an alkylene group containing from 2 to 6 carbon atoms or a groupof the structure and R and R are independently selected from the groupconsisting of hydrogen and alkyl of from 1 to 4 carbon atoms.

2. The method as claimed in claim 1 wherein the sulfur containingcompound is present in the electroplating bath in an amount within therange of about 0.01 to about 0.4 grams per liter.

3. The method as claimed in claim 1 wherein the sulfur containingcompound is present in the electroplating bath from which theintermediate nickel containing layer is produced in an amount within therange of about 0.03 to 0.1 grams per liter.

4. The method as claimed in claim 1 wherein the sulfur containingcompound is present in the electroplating bath from which the uppernickel containing layer is produced in an amount within the range ofabout 0.01 to 0.04 grams per liter.

5. The method as claimed in claim 1 wherein the sulfur containingcompound is the thiosulfonate of Formula A.

6. The method as claimed in claim 1 wherein the sulfur containingcompound is the thiosulfonate of Formula B.

7. The method of claim 1 wherein the sulfur containing compound is thethiosulfonate of Formula C.

8. The method of claim 1 wherein the thiosulfonate compound is of theformula:

H H H 9. The method of claim 1 wherein the thiosulfonate compound is ofthe formula:

10. The method of claim 1 wherein the thiosulfonate is of the formulastructure:

11. The method of claim 1 wherein the thiosulfonate is of the structure:

12. An electroplating bath suitable for forming a nickel containingelectroplated layer for a composite coating which comprises an aqueousacidic solution of nickel salts and a thiosulfonate of nitriles oramides in an amount to provide a sulfur content in the electroplatedlayer of from about 0.02 to 0.3%; said thiosulfonate being selected fromthe group consisting of:

wherein R is an alkylene group containing 2 to 4 carbon atoms; R iseither an alkylene group containing from 2 to 6 carbon atoms or a groupof the structure and R and R are independently selected from the groupconsisting of hydrogen and alkyl of from 1 to 4 carbon atoms.

13. The electroplating bath as claimed in claim 12 wherein the organicsulfur containing compound is present in the bath in an amount withinthe range of about 0.01 to 0.4 grams per liter.

14. The electroplating bath as claimed in claim 12 wherein the organicsulfur containing compound is the thiosulfonate of Formula A.

15. The electroplating bath as claimed in claim 12 wherein the organicsulfur containing compound is the thiosulfonate of Formula B.

16. The electroplating bath of claim 12 wherein the organic sulfurcontaining compound is the thiosulfonate of Formula C.

17. The electroplating bath of claim 12 wherein the thiosulfonatecompound is of the formula:

18. The bath of claim 12 wherein the thiosulfonate compound is of theformula 9 19. The electroplating bath of claim 12 wherein thethiosulfonate compound is of the formula:

20. The electroplating bath of claim 12 wherein the 5 UNITED STATESPATENTS 2,830,014 4/1958 Giindel et a1. 204'49 2,972,571 2/ 1961 Towle20449 1 2,978,391 4/1961 Du l me 20449 2,994,648 8/1961 Du Rose 204-493,000,799 9/ 1961 Towle 204-49 3,090,733 5/1963 Brown 20440 GERALD L.KAPLAN, Primary Examiner US. Cl. X.R.

